Cryogenic cooling apparatus for radiation detector

A radiation detector cryogenic cooling apparatus is described comprising: first, second and third thermally conductive tubular members secured in nested concentric spaced relation, said first member being external and the third member being positioned innermost in said spaced relation; means for securing the first member in substantial thermal conductive isolation relative to the other members; means for coupling one end of the second and third members to a source of cryogenic cooling; and means for securing a radiation detector to the third member at the other end opposite the one end, said first member exhibiting the highest temperature and the third member exhibiting the lowest temperature and a negligible temperature gradient between said one and other ends